Tbf, the backless or the very-low cut, the strapless and super sexies IMO do not really go with a church wedding anyway. Afterall the church is very conservative and eg. doesn't allow tourists in with bare shoulders or too short skirts.
In the US, a lot of couples choose to have their nuptuals in a freer environment eg. a garden setting or a club, and then I think you are free to wear what you like. But if you choose that age-old, conservative and traditional setting, then (IMO!) you need to adjust.